Drip irrigation systems usually include a continuous irrigation water supply line with emitter-type drippers installed along the line, usually at regular intervals. Irrigation water flows through the supply line under pressure, and a small amount of water continuously drips out at the intervals where the drippers are located. Drip irrigation has proved to be highly successful in producing greater growth of vegetation with the same amount of water, when compared with conventional irrigation techniques.
A number of different drip irrigation systems have been used in the past. They vary from the cheapest and simplest systems, namely, a hole in the wall of a water supply line, to expensive and complex multi-component dripper units.
Perhaps the most practical of the prior drip irrigation systems involves use of separate drip emitters or drippers installed in or on the supply line. The dripper taps off a portion of the water flowing in the water supply line and passes the water through a labyrinth or other meandering or circuitous path that produces a large pressure drop in the water and discharges it at a uniform drip rate. Generally, such pressure-reducing labyrinthine drippers are successful because they use a large enough hole in the supply pipe and a wide enough passage through the labyrinth to avoid clogging in most cases, while they also operate at reasonably high line pressures.
The U.S.D.A. and other research groups have recognized that drip irrigation can provide savings benefits for water, agricultural chemicals, energy and labor; and that these benefits particularly apply to low value field crops, such as alfalfa, sugar cane, corn and cotton. Furthermore, they have shown that use of drip irrigation can result in a meaningful reduction in the pollution of aquifers by salts and agricultural chemicals.
The present invention is directed to the problem of developing an economic drip irrigation system for low value crops where it is essential to reduce the capital costs for a precise system to a level lower than that achieved by drip irrigation systems presently available.
There are low cost drip irrigation systems made from thin plastic film, as thin as 0.004 inch in wall thickness. These products are not easy to use because of the low strength of the film, and they are used for one growing season only and then thrown away. There are similar drip irrigation systems with wall thicknesses up to about 0.02 inch, and if buried, they will last for many crops, but these systems have problems with root intrusion. In addition, the management to operate these systems for several crops is very difficult, and thus excludes most growers. Drip irrigation systems presently on the market also do not effectively combine with the technology to use herbicides, such as trifluralin, to keep roots out of drip systems. U.S. Pat. No. 5,116,414 to Burton et al. describes a method for preventing roots of plants from intruding into a zone of soil below the surface of the soil without killing the plants. The patent describes a method for incorporating the herbicide trifluralin into a polymer to form a controlled release of trifluralin, which is EPA-registered for this application. Because of the low vapor pressure of trifluralin and its resultant volatility, it is very difficult to extrusion mold drip irrigation products containing trifluralin, because the heat of extrusion dissipates the trifluralin. Furthermore, due to the high cost of trifluralin, it is essential in its application to drip irrigation to maintain the trifluralin in the area to be protected, i.e., the exit holes from the drip system. For instance, it can be prohibitively expensive to uniformly disperse trifluralin in the wall of a drip irrigation conduit for the length of the supply line. There are heavy walled products with a wall thickness of 0.045 inch, for example, such as taught by Ruskin in U.S. Pat. No. 5,052,625, which are combined with trifluralin. However, these products are much too expensive for low value field crops.
Hence, there is a need for a low cost drip irrigation system having low manufacturing costs, including the costs of materials, capital and labor, and high production speeds. There is also a need for a low cost dripper system suitable to carry trifluralin so that it is effective during use, and so that the end product will deliver precise amounts at each orifice. Such low cost dripper systems should be resistant to clogging by impurities in the water. There is also a need for a low cost drip irrigation system that will have an extended life beyond the growing season of one crop and can, in fact, be used for multiple growing seasons or multiple crops in sequence over an extended period of time, while the trifluralin also remains effective over such an extended period of time.